docs: def clean_highlight(self):
          """
          Remove the empty highlight
          """
          if not self.valid:
              return
  
          for hit in self._results['hits']['hits']:
              if 'highlight' in hit:
                  hl = hit['highlight']
                  for key, item in list(hl.items()):
                      if not item:
                          del hl[key]